1. Field of the Invention
This invention relates to an epitaxial wafer manufacturing apparatus and manufacturing method.
2. Background Art
Epitaxial growth for vapor-phase growth of a single crystal film on a semiconductor substrate such as a silicon wafer is often based on the CVD (chemical vapor deposition) method. In an epitaxial wafer manufacturing apparatus based on CVD, for example, a rotating unit is located in a chamber, a wafer holder, which is annular, for example, for holding a wafer is provided on the upper surface of the rotating unit, and a heater for heating the wafer is provided in the rotating unit. A raw material gas is introduced into the chamber to produce a single crystal film on the wafer while rapidly rotating the wafer together with the rotating unit.
In producing a single crystal film on a wafer, if, for example, trichlorosilane is used as a raw material gas and hydrogen is used as a carrier gas, then a reacted gas such as chlorine is generated.
It is desirable that this reacted gas be smoothly exhausted to the exhaust port. However, in conventional epitaxial wafer manufacturing apparatuses, the wafer and the wafer holder are rapidly rotated with the rotating unit, and hence a centrifugal force occurs in the reacted gas. Accordingly, near the outer edge of the rotating unit, this reacted gas has an increased flow velocity toward the outer periphery, which sometimes results in backflow of the reacted gas onto the wafer. The backflow reacted gas etches the silicon film and interferes with improvement in growth rate and gas utilization efficiency.
Furthermore, film formation of multiple layers requires switching the dopant gas concentration and dopant gas species. The conventional epitaxial wafer manufacturing apparatus has poor replacement efficiency of gas in the apparatus, and hence requires a long period of time to switch the concentration or species of the dopant gas. This decreases throughput, and consequently interferes with improvement in the productivity of epitaxial wafers.
In this context, JP-A 2001-140078(Kokai) discloses a technique related to a chemical vapor deposition apparatus. In this technique, a gas flow-regulating plate is provided between the substrate and a gas introducing guide shaped so that its distance to the substrate is gradually narrowed above the substrate. The gas flow-regulating plate serves to prevent circulating flow of the raw material gas to make the film thickness uniform. However, this technique is intended to control the flow of the raw material gas, and cannot control the aforementioned reacted gas.